The present invention pertains generally to the art of endless chain conveyors and, more specifically, to conveyors of the type utilizing two parallel strands of chain with conveyor flights attached therebetween and supported for movement by a series of rollers mounted on each strand of chain. The invention herein relates particularly to roller assemblies for use in such conveyors.
A wide variety of chains and conveyor flights are known in the art because of the extremely wide range of materials which may be conveniently conveyed in this manner. One type of conveyor widely used to convey bulk materials is commonly known in the art as an apron conveyor or a pan conveyor. This type of conveyor utilizes a series of open-ended overlapping pans mounted between two parallel strands of chain to provide a continuous substantially flat conveying surface. The conveyor chains are supported by rollers which operate over a pair of rails along the conveyor path. The supporting rollers may be of the "inboard" type wherein they are mounted on the conveyor chain bushings between the chain sidebars, as shown for example in U.S. Pat. No. 3,331,490; or they may be of the "outboard" type wherein the rollers are mounted on the outside of the conveyor chain sidebars, most commonly in pairs on a shaft extending through the sidebars thereof, as shown for example in U.S. Pat. No. 2,517,208.
In apron conveyors using an outboard roller construction, the rollers are commonly made of cast iron and are provided with cylindrical through bores which are mounted for rotation on plain cylindrical iron or steel bushings. Pairs of bushings and rollers are mounted on ends of the shaft and outwardly of the respective chain sidebars, as is shown in the above mentioned U.S. Pat. No. 2,517,208. Preferably, some means of securing the bushings against rotation on the common shaft is used and thus the roller rotates on the bushing in the manner of a plain journal bearing. Square shaft ends and corresponding square bores in the bushings are an example of one means of preventing bushing rotation, such as shown in U.S. Pat. No. 3,214,008.
Such cast iron rollers have been widely accepted as inexpensive, strong and durable components in apron conveyors used to convey a wide variety of bulk materials, such as castings, sugar cane, solid waste, limestone, coal and other minerals and ores. Most of these materials are, however, dusty, dirty, or highly abrasive and these contaminants inevitably work their way during operation of the conveyor into the bearing areas between the rollers and bushings, resulting in wear and eventual failure of the roller assembly. The rollers may be provided with internal grease cavities or reservoirs which are periodically regreased via an external grease fitting and some of the foreign material will be purged in the regreasing process. However, not only is such purging less than completely effective, but the basic problem of immediate re-entry of contaminants remains.
An effective means of sealing the bearing area against contaminant entry has therefore been long sought in the art. Labyrinth seals of many types are well known in the bearing art, however, the complex constructions and high cost of these seals make them generally unsuitable for use in roller assemblies of the type disclosed herein. U.S. Pat. No. 3,490,773 discloses a labyrinth seal for use in a cast iron roller of the type used in an outboard roller assembly of an apron conveyor. The labyrinth is comprised of two spaced rings, one fitted to the outside diameter of the bushing and the other to the inside diameter of a counterbore in the roller member. The two rings form a two-chamber labyrinth which, when filled with grease in the lubrication process, is intended to prevent the entry of contaminants from outside the assembly. However, since neither sealing ring is fitted tightly to the bushing or the roller, respectively, the resultant clearances in seal constructions of this type can allow "short circuiting" of the labyrinth and direct entry of contaminants along the bushing surface into the bearing area.
Seals of the general type heretofore described also exhibit two other deficiencies. First, loose fitting sealing rings must be retained in place by additional retaining means, such as a snap ring, thus adding to the complexity and cost of the assembly. Second, the lateral thrust loads often imposed on rollers in operation require a substantial thrust bearing surface which has been deficient or totally lacking in prior art constructions.